A conventional receiver is explained below. Conventional receivers are described, for example, in “Experimental Evaluation on Coherent Adaptive Array Antenna Diversity for DS-CDMA Reverse Link, The Institute of Electronics, Information and Communication Engineers, Technical Report of IEICE, RCS98-94, p. 33-38, September, 1998”, and “Laboratory Experiments on Coherent Rake Receiver in Broadband DS-CDMA Mobile Radio, The Institute of Electronics, Information and Communication Engineers, Technical Report of IEICE, CS99-129, p. 57-62, October, 1999”.
FIG. 9 shows the configuration of the conventional receiver. In FIG. 9, 201-1, 201-2, . . . 201-N denote N antennas, 202-1, 202-2, . . . , 202-N denote N band-pass filters (hereinafter, “BPF”), 203-1, 203-2, . . . , 203-N denote N despreading sections, 204 denotes a path detector, 205-1, 205-2, . . . , 205-L denote L beam forming sections that receive despread signals affected by multipath waves, to form beams for each path with respect to L paths, 206 denotes an adder, and 207 denotes a data judging section.
In each beam forming section, 221-1, 221-2, . . . , 221-N denote N complex multipliers, 222 denotes a delay device, 223 denotes a weight controller, 224 denotes an adder, 225 denotes a complex multiplier, 226 denotes a complex conjugate calculator, 227 denotes a complex multiplier, 228 denotes a subtracter, and 229 denotes a transmission line estimating section that estimates a transmission line with respect to the individual path.
FIG. 10 shows a detailed configuration of the path detector 204. In the path detector 204, 300 denotes a transmission line estimating section, 301 denotes a mean power value calculator, 302 denotes a threshold calculator, 303 denotes a judging section, and 304 denotes a path selecting section, which detects a plurality of paths from the despread signal.
FIG. 11 shows a format of a transmission slot. The transmission slot comprises a pilot symbol portion (known sequence) and a data portion. FIG. 12 shows one example of impulse response of the transmission line of frequency selective fading. In the mobile communication system, waves (multipath waves) having passed through a plurality of transmission lines arrive due to reflection, diffraction, and scattering of radio-waves resulting from the surrounding buildings and geographical features, and interfere with each other. Here is shown a case in which a signal that has become a multipath wave is input to a reception antenna.
The operation of the conventional receiver is explained next, with reference to FIG. 9 and FIG. 10. Signals from a mobile station received by N antennas 201-1 to 201-N are filtered by the BPFs 202-1 to 202-N, respectively, so that a desired band limitation is applied thereto. The despreading sections 203-1 to 203-N having received the band restricted signals perform despreading, using the same sequence as the spreading code sequence used on the transmission side.
The path detector 204 selects L paths from the despread signals affected by the multipath waves, using one antenna output. Specifically, in the path detector 204, at first, the transmission line estimating section 300 uses a pilot symbol provided for each slot, to perform in-phase addition of all symbols in one slot to thereby obtain a momentary estimate of the transmission line. The mean power value calculator 301 performs power averaging processing over several slots, using the transmission line estimate, to thereby calculate a mean power delay profile. The threshold calculator 302 regards power in the path having the smallest power in the mean power delay profile as noise, and designates power larger by AdB than the power in the path having the smallest power as a threshold for path selection. The judging section 303 compares the mean power delay profile with the threshold, and designates the path having a mean power value larger than the threshold as a multipath with respect to a desired signal, and outputs timewise position information and path power value of the path.
The respective beam forming sections generally perform signal processing with respect to predetermined L paths, due to a limitation in hardware or software. Therefore, in the path detector 204, at the end, the path selecting section 304 selects L effective paths in decreasing order of mean power value. The timewise position of the selected path is output to the respective beam forming sections as the path position information. The despread signals are separated for each path detected by the path detector 204, and transmitted to the beam forming sections 205-1 to 205-L.
The beam forming sections 205-1 to 205-L form beams for each detected path. Here, the beam forming section 205-1 performs the signal processing with respect to the first path, and the beam forming sections 205-2 to 205-N sequentially perform the signal processing with respect to the second to the L-th path.
The operation of the respective beam forming sections is explained in detail below. The weight controller 223 calculates a weight based on the adaptive algorithm such as Least Mean Square (LMS), and the complex multipliers 221-1 to 221-N multiply the signals received from the respective antennas by a complex weight for forming beams. The adder 224 combines the signals output from the complex multipliers to generate a signal after the antenna combine, having directivity.
The transmission line estimating section 229 uses a pilot symbol provided for each slot (see FIG. 11), to calculate a transmission line estimate (complex value) for the first path. The complex conjugate calculator 226 calculates a complex conjugate of the transmission line estimate. The complex multiplier 225 multiplies the complex conjugate by the combined signal output from the adder 224, and outputs a signal weighted in proportion to the signal amplitude, with phase fluctuation being removed.
The adder 206 having received signals from the first to the L-th paths at the same time combines the phase-matched signals for each path. Lastly, the data judging section 207 performs hard judgment with respect to the output from the adder 206, and outputs the result as a demodulation result. Since the demodulation result is used as a reference signal at the time of forming beams for each path, it is branched and transmitted to the respective beam forming sections.
A method of determining a weight for each antenna by the adaptive algorithm is explained below, using the beam forming section 205-1 corresponding to the first path. At first, the complex multiplier 227 performs complex multiplication of the output from the data judging section 207 and the output from the transmission line estimating section 229, to generate the reference signal. The subtracter 228 performs subtraction processing of the output from the complex multiplier 227 and the output from the adder 224, to generate an error signal e1*(k) with respect to the first path. Lastly, the weight controller 223 receives the error signal e1*(k), and updates the weight as shown in the following equation (1), based on the normalized LMS in the adaptive algorithm:                                           W            1                    ⁡                      (                          k              +              1                        )                          =                                            W              1                        ⁡                          (              k              )                                +                      μ            ⁢                                                            X                  1                                ⁡                                  (                                      k                    -                    τ                                    )                                                                                                                                          X                      1                                        ⁡                                          (                                              k                        -                        τ                                            )                                                                                        2                                      ⁢                                          e                1                *                            ⁡                              (                k                )                                                                        (        1        )            wherein ∥·∥ denotes a norm, k corresponds to the k-th sampling time (t=kTs: Ts denotes a sampling period), and * denotes a complex conjugate. X1(k) is a vector expression of the first path of the despread signals received by the respective antennas, and is such that X1(k)=[x1(1, k), x1(2, k), . . . , x1(N, k)]T, W1(k) is a vector expression of the weight for each antenna with respect to the first path, and is such that W1(k)=[w1(1, k), w1(2, k), . . . , w1(N, k)]T. The initial value of W1(k) is W1(0)=[1, 0, . . . , 0]T, μ denotes a step size, and τ denotes delay time necessary for a series of processing until the signal is input to the weight controller 223.
In the transmission line of frequency selective fading, the conventional receiver improves signal to interference ratio (SIR) relating to a desired signal, using a method in which the adaptive algorithm is used with respect to the path-detected L paths, to form beams separately, and weighting combine (RAKE combine) is performed corresponding to the transmission line estimate, while directing null to the interference signal.
In the conventional receiver, however, since the incoming direction of the multipath from a mobile station to the base station cannot be known, in the initial state before forming the beams by the adaptive array antennas, beams having sharp directivity cannot be formed, and one antenna having broad directivity is used. Therefore, when path detection is performed by one antenna, and when the interference quantity is large, there is a problem in that path detection cannot be performed at high accuracy, corresponding to the signal quality in the path.
In the conventional receiver, from a reason similar to the above, an initial value of the weight is set so as to use one antenna, in the initial state when beams are formed by the adaptive array antennas. In this case, since much time is required for the processing of forming beams based on the adaptive algorithm, on the transmission side of the mobile station, much transmission signal power is required so that the required quality can be satisfied on the reception side of the base station, while signal processing until finishing beam formation is performed on the base station side. Therefore, on the reception side of the base station, the interference power increases momentarily, thereby making it difficult to obtain ideal channel capacity.
In the conventional receiver, it is necessary to prepare one adaptive algorithm for each of the detected L paths, and hence there is a problem in that the hardware size increases.
In the conventional receiver, it is necessary to operate the adaptive algorithm even for a path having a small reception power, if it is the detected path. Therefore, the time required until the adaptive algorithm is settled increases, and hence there is a problem in that the interference power cannot be sufficiently suppressed until the settlement.
It is therefore an object of the present invention to provide an adaptive antenna receiver that can realize highly accurate path detection corresponding to the signal quality in the path and an improvement in reception quality, and can realize a reduction in the hardware and software size.
The adaptive antenna receiver according to one aspect of the present invention comprises a beam forming unit that uses a plurality of antennas to forms beams having fixed directivity; a plurality of despreading units that separately despread a beam signal corresponding to the beams having fixed directivity; a path detecting unit that detects multipath waves on a transmission line based on the signals obtained by despreding, and outputs path position information as a detection result; a transmission line estimating unit that estimates a transmission line for transmitting an adaptive beam combined signal for each path, based on the path position information; a plurality of complex multiplication units each of which separately complex multiplies the despread signals by the transmission line estimation result for each path; an adaptive beam forming unit that generates a weight for each path by operating an adaptive algorithm for each path, using a plurality of complex multiplication results and data judgment results in each path, and forms an adaptive beam combined signal for each path, using the weight and the despread signals; a phase matching unit that performs phase matching corresponding to the transmission line estimated by the transmission line estimating unit, using the adaptive beam signal for each path; a path combining unit that combines the adaptive beam signals after phase matching for all paths; and data judging unit that judges the data included in the adaptive beam signals combined.
The adaptive antenna receiver according to another aspect of the present invention comprises a beam forming unit that uses a plurality of antennas to form beams having fixed directivity; a plurality of despreading units that separately despread a beam signal corresponding to the beams having fixed directivity; a path detecting unit that detects multipath waves on a transmission line based on the signals obtained by despreding, and outputs path position information and predetermined beam selection information necessary for operating the adaptive algorithm as a detection result; a transmission line estimating unit that estimates the transmission line for transmitting an adaptive beam combined signal for each path, based on the path position information; a plurality of complex multiplication units each of which separately complex multiplies the despread signal by the transmission line estimation result for each path; an adaptive beam forming unit that generates a weight common to all paths by operating one adaptive algorithm, using the complex multiplication results, data judgment results, and the beam selection information for all paths, and forms an adaptive beam combined signal for each path, using the weight common to all paths and the despread signals; a phase matching unit that performs phase matching corresponding to the transmission line estimated by the transmission line estimating unit, using the adaptive beam signal for each path; a path combining unit that combines the adaptive beam signals after phase matching for all paths; and a data judging unit that judges the data included in the adaptive beam signals combined.